U.S. Pat. No. 6,311,847 discloses a method and means for sand reblending using a single tank for receiving aggregate of various sizes for classification. The tank has a plurality of stations with primary and secondary discharge valves. The tank is then calibrated to determine raw feed analysis, discharge rates and the flow multipliers needed to develop a mathematical model of the tank. Inputting the calibration information data and the desired production specification into a computer allows the tank to be operated and controlled with appropriate adjustments in discharge rates and valve percent settings at each station. The apparatus for this method includes the tank, a pumping device, and a computer interconnected with a PLC and electrohydraulic mechanisms for valves at each tank station such that both the discharge rate from each station and the valve percent settings of the individual valves at each station are variable and controllable.
It is common in sand reblending to use two or more classification tanks. Currently the available systems for controlling multiple classifying tanks are to use multiple controls. These separate controls blend a specification material and then the two materials are mechanically blended into one presumably specification product. This is a good assumption as long as the material being fed to the tanks is the same. If this material is dissimilar either due to mechanical means or is from different sources then the efficiency of the twin tanks can be severely impaired and it is theoretically possible that a combined product will be out of specification. Finally, control of the fineness modulus (another type of specification designed to make the output of a plant consistent from day to day) is problematic and would require human oversight.
It is therefore an object of the invention to provide a method and means for sand reblending wherein multiple tanks operate in accordance with the process of U.S. Pat. No. 6,311,847 but are controlled by a single controller so that the tanks act concurrently and in unison as if they were one large tank.
A further object of the invention is to provide a method and means for sand reblending which improves the efficiency of the tanks and wherein shortages in one tank may be offset by excesses in the other.
These and other objects will be apparent to those skilled in the art.